(a) Field of the Invention
The present invention relates to a single shaft rotary grinder with an improved cutter and combination “comb” rotor and counter knife configuration for reducing film, fibrous material and other material which has a tendency to wrap around the rotor, rubber, solid plastics and wood. Reducing this type of material, such as plastic film, into small pieces has been problematic. This invention provides one or more comb shaped counter knives and a rotor having a plurality of geometrically shaped cutters mounted in a plurality of partial or full rows longitudinally along the rotor. The comb shaped counter knives and the rows of cutters work in cooperation to reduce film and other material into small pieces.
(b) Description of the Prior Art
U.S. Pat. No. 3,760,673, to Peterson, Jr. teaches an apparatus for dicing plastic sheet material, rather than film or fibrous material, in which a horizontal rotor has teeth on the periphery thereof which are in cutting relationship to the serrations on a stationary bed knife. The bed knife is tilted at an angle to the axis of the rotor. The rotor contains a series of straight knives which each contain a plurality of teeth which cooperate with the serrations on the stationary bed knife. The tilt of the bed knife causes the teeth of each rotor knife to first come into cutting engagement with the bed knife teeth at the left end of the bed knife and then to be brought into cutting engagement last with the teeth at the right end of the bed knife.
U.S. Pat. No. 3,186,277 to Brunner teaches an apparatus for cutting a strip of sheet material, rather than film or fibrous material, into separate particles which has a stationary bed knife having rectangular teeth and individual rectangular recesses between the teeth, a knife supporting rotor arranged axially parallel to the bed knife, and profiled knives on the rotor arranged in axially and angularly spaced relation with each cooperating with one of said recesses between the teeth of the stationary bed knife. The rotor also contains straight knives arranged in axially and angularly spaced relation which cooperate with the top of at least two teeth of the stationary bed knife.
U.S. Pat. No. 2,812,815 to Quinsey et al. teaches a method and apparatus for dicing a strip of sheet material, rather than film or fibrous material, into uniform sized and shaped pellets, both employing a bed knife with rectangular shaped teeth and a non-cylindrical rotor containing sets of fly knives, where each set of fly knives is comprised of a toothed knife with teeth complementary to the bed knife teeth and a cut off knife having a continuous linear cutting edge which cooperates with the front edge of the bed knife.
U.S. Pat. No. 1,874,902 to Clyne teaches a method of cutting sheets and a sheet cutting machine employing a cutter bar having substantially rectangular shaped teeth and rectangular shaped notches therebetween, all with cutting edges and a cutter with a plurality of rows of teeth with notches therebetween which correspond to the notches and teeth of the cutter bar During engagement, the cutter teeth do not fully engage the length of the notches on the cutter bar. Between each engagement of the row of teeth on the cutter with the cutter bar, the sheet to be cut is fed forward less than the length of a tooth on the cutter bar, thereby allowing only that portion of the sheet which has been fed past the edge of the cutter bar teeth and notches to be engaged by a row of teeth on the cutter bar. The size of the particle cut from the sheet is therefore controlled by how the material is fed towards the rotor.
Reducing product such as film utilizing the single shaft rotary grinders present in the field today is problematic. Film for products such as plastic bags, plastic wrapping, garbage bags and sandwich bags and fibrous material such as rope and string have increasingly been manufactured with qualities of reduced thickness (less than 0.0254 mm (0.001 inches)) and increased durability, which cause the product to be more difficult to reduce. A common problem arises when the product wraps around the rotor with the cutter poking through the product, rather than being reduced into smaller pieces. An additional problem is created when, due to wrapping, the diameter of the product build-up is increased to the point that rubbing occurs, generating heat which may cause melting or other damage to the grinder. Another problem occurs because the combination of rotor and screen, with specific screen hole sizes, is inefficient in controlling reduction of the product to a maximum size, thus adding frictional heat to the process.